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Inside System Storage -- by Tony Pearson

Tony Pearson is a Master Inventor and Senior IT Specialist for the IBM System Storage product line at the
IBM Executive Briefing Center in Tucson Arizona, and featured contributor
to IBM's developerWorks. In 2011, Tony celebrated his 25th year anniversary with IBM Storage on the same day as the IBM's Centennial. He is
author of the Inside System Storage series of books. This blog is for the open exchange of ideas relating to storage and storage networking hardware, software and services. You can also follow him on Twitter @az990tony.
(Short URL for this blog: ibm.co/Pearson
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I didn't really have a theme this week, still recovering from jet-lag from my travels through Japan, Australia, China.

Gary Diskman has an amusing blog entry about a Funny disaster recovery job posting. It is not clear if he is being completely tongue-in-cheek, or a bit cynical. However, it rings true that you get what you measure, and some managers look for easy metrics, even if there are unintended consequences.

Western medicine works this way. Rather than paying your doctor to keep you healthy, you pay him per visit, to get refills on prescriptions, check-ups on medical conditions, surgeries and so on. While Eastern medicine is focused on keeping people healthy, Western medicine profits more from resolving "situations".

I have seen similar situations on the "health" of the data center. In one case, the admins were measured on how quickly they bring back up their web-servers after a crash. They had this process down to a science, because they were measured on how quickly they resolved the situation. I suggested switching from Windows to Linux, a much more reliable operating system for web-serving, and showed examples of web-servers running Linux that have been up for 1000 days or more. Management changed the metrics to "average up-time in days" and magically the re-boots all but disappeared, thanks to Linux, but also thanks in part to shifting the incentive structure. Perhaps some of those earlier situations were "artificially created"?

Back in the 1980s, I was working on a small software project that was about 5000 lines of code. In those days, testers were measured by the number of "successful" testcases that ran without incident. Testcases that uncovered an error were labeled as "failures" to be re-run after the developers fixed the code. When I declared my code ready for test, the test team ran 110 testcases, all successfully, and they were all rewarded for meeting their schedule. I, on the other hand, did not accept these results, met with them and told them I would give them $100 each if they could find a bug in my code in the next week. Nobody writes 5000 lines of code without some error along the way, not even me. (As one author put it, more people have left earth's gravity to orbit the planet than have written perfect code that did not require subsequent review or testing. It's so true. Good software is difficult to write.)

The test team accepted the challenge, and found 6 problems, more than I expected, but at least I felt more confident of the code quality after fixing these. As I suspected, the unintended consequence of counting "successful" testcases was that testers would write the most simple, basic, least-likely-to-challenge-boundaries testcases to ensure they meet their numbers. My experiment was costly to me, but more importantly was a wake-up call for the test management, and they realized they needed to re-evaluate their test procedures, metrics and terminology. This was a long time ago, and I am glad to see that the overall "software engineering" practice has matured much over the past 20 years.

So, my advice is to determine metrics that have the intended consequences you want, while avoiding any negative unintented consequences that might undermine your eventual success. People will quickly figure out how to maximize the results, and if you can align their goals to company goals, then everybody benefits.

Well, I'll be blogging from Mexico next week (yes, it is a business trip!). Enjoy the weekend.

While most of the post is accurate and well-stated, two opinions particular caught my eye. I'll be nice and call them opinions, since these are blogs, and always subject to interpretation. I'll put quotes around them so that people will correctly relate these to Hu, and not me.

"Storage virtualization can only be done in a storage controller. Currently Hitachi is the only vendor to provide this."-- Hu Yoshida

Hu, I enjoy all of your blog entries, but you should know better. HDS is fairly new-comer to the storage virtualization arena, so since IBM has been doing this for decades, I will bring you and the rest of the readers up to speed. I am not starting a blog-fight, just want to provide some additional information for clients to consider when making choices in the marketplace.

First, let's clarify the terminology. I will use 'storage' in the broad sense, including anything that can hold 1's and 0's, including memory, spinning disk media, and plastic tape media. These all have different mechanisms and access methods, based on their physical geometry and characteristics. The concept of 'virtualization' is any technology that makes one set of resources look like another set of resources with more preferable characteristics, and this applies to storage as well as servers and networks. Finally, 'storage controller' is any device with the intelligence to talk to a server and handle its read and write requests.

Second, let's take a look at all the different flavors of storage virtualization that IBM has developed over the past 30 years.

1972

IBM introduces the S/370 with the OS/VS1 operating system. "VS" here refers to virtual storage, and in this case internal server memory was swapped out to physical disk. Using a table mapping, disk was made to look like an extension of main memory.

1974

IBM introduces the IBM 3850 Mass Storage System (MSS). Until this time, programs that ran on mainframes had to be acutely aware of the device types being written, as each device type had different block, track and cylinder sizes, so a program written for one device type would have to be modified to work with a different device type. The MSS was able to take four 3350 disks, and a lot of tapes, and make them look like older 3330 disks, since most programs were still written for the 3330 format. The MSS was a way to deliver new 3350 disk to a 3330-oriented ecosystem, and greatly reduce the cost by handling tape on the back end. The table mapping was one virtual 3330 disk (100 MB) to two physical tapes (50 MB each). Back then, all of the mainframe disk systems had separate controllers. The 3850 used a 3831 controller that talked to the servers.

1978

IBM invents Redundant Array of Independent Disk (RAID) technology. The table mapping is one or more virtual "Logical Units" (or "LUNs") to two or more physical disks. Data is striped, mirrored and paritied across the physical drives, making the LUNs look and feel like disks, but with faster performance and higher reliability than the physical drives they were mapped to. RAID could be implemented in the server as software, on top or embedded into the operating system, in the host bus adapter, or on the controller itself. The vendor that provided the RAID software or HBA did not have to be the same as the vendor that provided the disk, so in a sense, this avoided "vendor lock-in".Today, RAID is almost always done in the external storage controller.

1981

IBM introduces the Personal Computer. One of the features of DOS is the ability to make a "RAM drive". This is technology that runs in the operating system to make internal memory look and feel like an external drive letter. Applications that already knew how to read and write to drive letters could work unmodified with these new RAM drives. This had the advantage that the files would be erased when the system was turned off, so it was perfect for temporary files. Of course, other operating systems today have this feature, UNIX has a /tmp directory in memory, and z/OS uses VIO storage pools.

This is important, as memory would be made to look like disk externally, as "cache", in the 1990s.

1990

IBM AIX v3 introduces Logical Volume Manager (LVM). LVM maps the LUNs from external RAID controllers into virtual disks inside the UNIX server. The mapping can combine the capacity of multiple physical LUNs into a large internal volume. This was all done by software within the server, completely independent of the storage vendor, so again no lock-in.

1997

IBM introduces the Virtual Tape Server (VTS). This was a disk array that emulated a tape library. A mapping of virtual tapes to physical tapes was done to allow full utilization of larger and larger tape cartridges. While many people today mistakenly equate "storage virtualization" with "disk virtualization", in reality it can be implemented on other forms of storage. The disk array was referred to as the "Tape Volume Cache". By using disk, the VTS could mount an empty "scratch" tape instantaneously, since no physical tape had to be mounted for this purpose.

Contradicting its "tape is dead" mantra, EMC later developed its CLARiiON disk library that emulates a virtual tape library (VTL).

2003

IBM introduces the SAN Volume Controller. It involves mapping virtual disks to manage disks that could be from different frames from different vendors. Like other controllers, the SVC has multiple processors and cache memory, with the intelligence to talk to servers, and is similar in functionality to the controller components you might find inside monolithic "controller+disk" configurations like the IBM DS8300, EMC Symmetrix, or HDS TagmaStore USP. SVC can map the virtual disk to physical disk one-for-one in "image mode", as HDS does, or can also map virtual disks across physical managed disks, using a similar mapping table, to provide advantages like performance improvement through striping. You can take any virtual disk out of the SVC system simply by migrating it back to "image mode" and disconnecting the LUN from management. Again, no vendor lock-in.

The HDS USP and NSC can run as regular disk systems without virtualization, or the virtualization can be enabled to allow external disks from other vendors. HDS usually counts all USP and NSC sold, but never mention what percentage these have external disks attached in virtualization mode. Either they don't track this, or too embarrassed to publish the number. (My guess: single digit percentage).

Few people remember that IBM also introduced virtualization in both controller+disk and SAN switch form factors. The controller+disk version was called "SAN Integration Server", but people didn't like the "vendor lock-in" having to buy the internal disk from IBM. They preferred having it all external disk, with plenty of vendor choices. This is perhaps why Hitachi now offers a disk-less version of the NSC 55, in an attempt to be more like IBM's SVC.

IBM also had introduced the IBM SVC for Cisco 9000 blade. Our clients didn't want to upgrade their SAN switch networking gear just to get the benefits of disk virtualization. Perhaps this is the same reason EMC has done so poorly with its "Invista" offering.

So, bottom line, storage virtualization can, and has, been delivered in the operating system software, in the server's host bus adapter, inside SAN switches, and in storage controllers. It can be delivered anywhere in the path between application and physical media. Today, the two major vendors that provide disk virtualization "in the storage controller" are IBM and HDS, and the three major vendors that provide tape virtualization "in the storage controller" are IBM, Sun/STK, and EMC. All of these involve a mapping of logical to physical resources. Hitachi uses a one-for-one mapping, whereas IBM additionally offers more sophisticated mappings as well.

In case you haven't noticed, IBM System Storage makes most of their announcements on Tuesdays. IBM announced a lot today, so here is a quick run-down.

Cisco storage networking products

IBM continues to resell Cisco switches and directors, but now can offer these with a 1-year IBM warranty.

The entry-level Cisco 9124offers 8 to 24 ports. For IBM BladeCenter, IBM now offers the Cisco10-port and 20-port modules that slide into the back of the chassis, and are functionally equivalent to the 9124.The original BladeCenter came with a 16-port module with 14 internal, but only 2 external, which severely hamperedbandwidth connectivity to external storage. These new modules provide more external ports to relieve that constraint.

The midrange Cisco9200switches have two models, both with 16 fixed ports, with the option for a blade that can provide 12, 24 or 48 additional ports. The 9216A has 16 FCP ports, and the 9216i has 14 FCP ports, and 2 GbE ports to act as a router, such as toconnect to a remote location for business continuity using Metro Mirror or Global Mirror.

The new TS3400library is a small entry-level size library, supporting the enterprise-class TS1120 drive, providing interoperabilitywith the larger tape libraries, with all the support for tape encryption.

In addition to Linux, Unix, and WIndows, the TS1120 can now be connected to System i servers. In the past, the only IBMtape available to System i were the LTO models. There are a lot of businesses that need to comply with government regulations that are looking for tape encryption, and now IBM has made it accessible to more clients.

300GB drives at 15K RPM

The DS8000 can now support new drives with 300GB capacity at 15,000 RPM (15K). These can be up to 30 percent faster than the 10,000 RPM drives for typical workloads.

IBM continues its market leadership with these new set of features and offerings!

I am back from China, and now glad to be back in the old USA. Last week, someone asked me what would it take to add a specific feature to the IBM System Storage DS8300. The what-would-it-take question is well-known among development circles informally as a "sizing" effort, or more formally as "Development Expense" estimate.

For software engineering projects, the process was simply that an architect would estimate the number of "Lines of Code" (LOC) typically represented in thousands of lines of code (KLOC). This single number would convert to another single number, "person-months", which would then translate to another single number "dollars". Once you had KLOC, the rest followed directly from a formula, average or rule-of-thumb.

More amazing is that this single number could then determine a variety of other numbers, the number of total months for the schedule, the number of developers, testers, publication writers and quality assurance team members needed, and so on. Again, these were developed using a formula, developed and based on past experience of similar projects.

Hardware design introduces a different set of challenges. When I was getting my Masters Degree in Electrical Engineering, it took myself and four other grad students a full semester just to design a six-layer, 900 transistor silicon chip, which could only perform a single function, multiply two numbers together.At IBM, another book that I was given to read was Soul of a New Machine, documenting six hardware engineers, and six software engineers, working long hours on a tight schedule to produce a new computer for Data General.

So why do I bring this up now? IBM architects William Goddard and John Lynott are being inducted posthumously this year into the prestigious National Inventors Hall of Fame for their disk system innovation.

Under the leadership of Reynold Johnson, the team developed an air-bearing head to “float” above the disk without crashing into the disk. Imagine a fighter airplane flying full speed across the country-side at 50 feet off the ground. If you every heard the term "my disk crashed", it was originally referring to the read/write head touching the disk surface, causing terrible damage.

A uniformly flat disk surface was created by spinning the coating onto the rapidly rotating disk, leaving many wearing lab coats covered with disk liquid at waist level. Developing disk-to-disk and track-to-track access mechanisms proved more challenging, and nearly halted the project. The team, however, was adamant that this problem could be solved, and customers were increasingly asking for random access technology. The result was the "350 Disk Storage Unit" designed for the "305 RAMAC computer", which I have talked about a lot last year as part of our "50 years of disk systems innovation" celebration.

Neither Goddard nor Lynott had computing experience prior to joining IBM. Goddard was a former science teacher who briefly worked in aerospace. Lynott had been a mechanic in the Navy and later a mechanical engineer. They didn't have a nice formula based on past experience, they didn't have the benefit of Fred Brooks' advice, or the rules-of-thumb or averages now used to estimate the size of projects. They had to break new ground.

Wrapping up my week in China, I read an article by Li Xing in the local "China Daily" about energy efficiency in buildings. She argues that it is not enough for a building to be energy-efficient on its own, but you have to consider the impact of the other buildings around. Does it reflect the sun so harshly into neighboring windows that people are forced to put up blinds and use artificial light? Does it block the sun, so that rooms that previously could be used with natural sunlight must now be artificially lit?

A similar effect happens with power and cooling in the data center. Servers and storage systems generate heat, and that heat affects all the other equipment in the data center. IBM has the most power-efficient and heat-efficient servers and storage, but that is not enough. You have to consider the heat generated by all systems that might raise overall temperature.

Research has indicated that water can remove far more heat per volume unit than air. For example, in order to disperse 1,000 watts, with 10 degree temperature difference, only 24 gallons of water per hour is needed, while the same space would require nearly 11,475 cubic feet of air. IBM's Rear Door Heat eXchanger helps keep growing datacenters at safe temperatures, without adding AC units. The unobtrusive solution brings more cooling capacity to areas where heat is the greatest -- around racks of servers with more powerful and multiple processors.

The CoolBlue portfolio of IBM innovations includes comprehensive hardware and systems-management tools for computing environments, enabling clients to better optimize the power consumption, management and cooling of infrastructure at the system, rack and datacenter levels. The CoolBlue portfolio includes IBM PowerConfigurator, PowerExecutive, and Rear Door Heat eXchanger.

The eXchanger works on standard 42U racks, and can help clients deal with the rapid growth of rack-mounted servers and storage on their raised floor. How cool is that!